CVE-2007-5424 in PHP
Summary
by MITRE
The disable_functions feature in PHP 4 and 5 allows attackers to bypass intended restrictions by using an alias, as demonstrated by using ini_alter when ini_set is disabled.
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Analysis
by VulDB Data Team • 07/29/2021
The vulnerability described in CVE-2007-5424 represents a critical flaw in PHP's security model that undermines the intended protection mechanisms designed to restrict dangerous functions. This issue affects PHP versions 4 and 5, where administrators attempt to enhance security by disabling potentially harmful functions through the disable_functions directive in php.ini configuration files. The flaw exploits a fundamental design oversight that allows attackers to circumvent these restrictions through the strategic use of function aliases, specifically leveraging ini_alter as a bypass mechanism when ini_set has been disabled. The vulnerability operates at the core of PHP's function call resolution system, where certain functions share underlying implementations but maintain distinct names that can be used interchangeably for exploitation purposes.
The technical implementation of this vulnerability stems from PHP's internal function handling architecture, which maintains aliases for many built-in functions to ensure backward compatibility and provide alternative naming conventions. When administrators configure disable_functions to restrict access to functions like ini_set, they fail to account for the existence of alternative function names that perform identical operations. The ini_alter function serves as a direct example of this bypass mechanism, as it operates on the same underlying system configuration parameters as ini_set but remains unaffected by the disable_functions restriction. This creates a dangerous loophole in PHP's security framework where attackers can execute privileged operations without proper authorization, effectively neutralizing the intended protection measures. The vulnerability is particularly concerning because it demonstrates how seemingly simple configuration restrictions can be bypassed through a deep understanding of the underlying system architecture and function relationships.
The operational impact of CVE-2007-5424 extends far beyond simple privilege escalation, as it fundamentally compromises the security posture of web applications running on affected PHP versions. Attackers can leverage this vulnerability to manipulate critical system configurations, potentially leading to complete system compromise and unauthorized access to sensitive data. The bypass capability allows malicious actors to execute arbitrary code, modify system settings, and gain persistent access to compromised systems. This vulnerability directly relates to CWE-254 in the Common Weakness Enumeration, which addresses security weaknesses in the use of insecure functions and the improper implementation of access control mechanisms. The impact is particularly severe in environments where PHP applications handle sensitive user data or critical business operations, as the vulnerability can be exploited to undermine the entire security infrastructure of the hosting environment.
From a threat modeling perspective, this vulnerability aligns with several techniques documented in the MITRE ATT&CK framework, particularly those related to privilege escalation and defense evasion. The ability to bypass function restrictions represents a classic defense evasion technique where attackers circumvent security controls by exploiting alternative pathways. The vulnerability also demonstrates a privilege escalation vector that can be used to move laterally within compromised systems. Organizations implementing PHP-based web applications must recognize that this vulnerability affects not just individual applications but the entire server infrastructure, as it allows attackers to manipulate system-wide configurations. The exploitability of this vulnerability is enhanced by the fact that many administrators may not be aware of the aliasing mechanisms that exist within PHP, making it particularly dangerous in environments with limited security awareness. Security professionals should consider this vulnerability as part of a broader assessment of PHP security configurations and recommend immediate mitigation strategies including software updates, proper configuration reviews, and comprehensive security testing to identify potential bypass mechanisms.